For generations, English teachers have drilled their students in the notion that English grammar has three verb tenses: past, present and future. Rubbish! English has two tenses, past and present. The idea of an English future tense seems to have arisen from false analogy with Latin, which does have one.
will is future tense isn't it? No!
But what about "will" you say. "Will" is future tense, isn't it?
No! Certainly we sometimes use "will" to talk about future time, but time and tense are not to be equated. Prove the difference to yourself - think about the time conveyed in the following sentences:
1. Hurry! The train leaves in five minutes.
2. Lisa can't watch TV until her grades improve.
3. When is the last day to register to vote?
4. She's going have a baby.
5. We're having pizza for dinner!
All of the preceding sentences describe future events, events that may occur in a few minutes, a few hours, or perhaps several months from the moment of speaking - yet you didn't see a single "will" in any of them. All of them are in some form of the present tense.
Now take a look at these sentences and determine the time frame:
6. Will you please pass the salt?
7. A lion will attack only if it's hungry.
8. No matter what, John just won't listen to anything I say.
9. The game will be finished by now.
Deciding the "when" of these sentences is a little problematic. Although they all contain "will," it's hard to make a good case that these sentences refer to future time. We could argue that sentence 6, a request, talks about the very immediate future; but we could just as easily have said: "Please pass the salt." With or without "will," the same time is intended. The use of "will" is not intended to indicate futurity here; instead it merely softens the request
Sentence 7 states a fact. We might argue that, since it acts as a prediction, futurity is indicated; but I prefer to think of the statement as a timeless occurrence - true in the past, present, or future. The use of "will" is insignificant here; we could substitute attacks for will attack with no change of meaning.
Sentence 8 is similar to sentence 7 in the question of time. It will be true in the future, but we also get the impression that it was true in the past and is true right now. In this sentence, however, "will" is important, not as an indicator of time, but as an indicator of willingness, or rather, lack of willingness. In the negative, "won't" is frequently used to indicate refusals. This sentence could be rephrased "...just refuses to listen...
"The words "by now" in the last sentence clearly refer to present time, regardless of the verb form. In this case, "will" is used for a prediction derived from a conclusion.
If the above examples have turned your notions of the English tense system topsy-turvey, then I have accomplished my goal. The examples I presented make it seem as if future time is indicated by present tense (true), and as if present time is indicated by "will" (sometimes true). Of course, I deliberately left out examples clearly signifying future time with "will." To be fair, I'll provide a couple now:
10. The President will present his plan to Congress tomorrow night.
11. No one knows when he will die.
We could have gotten around the use of "will" in these sentences, however, by rephrasing them with a present tense form of "be going to," a commonly-used phrase indicating futurity in English:
12. The President is going to present his plan to Congress tomorrow night.
13. No one knows when he's going to die.
Is there any difference of meaning in the two pairs? Context and intonation might make a difference, but in isolation it's fruitless to argue one way or the other. For the moment, let's assume each pair has the same basic meaning. In this case, the factor that probably influences a speaker's choice between the two is formality: "will" is more formal than "be going to." Sentence 10 might occur in a White House announcement or in a newspaper, while sentence 12 would more likely occur in conversation.
The "be going to" phrase occurs so often in conversational English that foreign students learn very early to say, "I'm gonna watch TV, he's gonna help me, we're gonna eat soon," etc. If only "be going to" and "will" were always interchangeable, learning to express future time in English would be far easier for foreigners. Rules exist, and to some extent are known to linguists, but this is hazy territory.
Below are two exercises taken from English Structure Focus, a textbook for foreigners; the object is to decide whether to use "will" or "be going to."
John: Barbara, I love you. ______ you marry me?
Barbara: No, John, I'm sorry. I ______ marry Charles.
WEDNESDAY NIGHT AT THE SPITZES:
Mrs. S: I have to go to a meeting tonight. _____ you wash the dishes, dear?
Mr. S: What? I washed them last night. You can wash them after the meeting.
Mrs. S: No, I'm too tired. I _____ go to bed early.
Mr. S: Oh, all right. I _____ wash them. But then you have to wash them tomorrow and the day after tomorrow.
As a native speaker of English, you should have found the exercise mindlessly simple, but do you know how you knew which form was correct? If you were a foreign student of English, you would have analyzed how definite or abstract the event seemed to be. "Be going to" occurs with more definite events: "I'm going to marry Charles" (it's already decided; there's no question about it). "Will" is used for less settled matters: "Will you marry me?"
Backtracking to sentences 11 and 13, let's speculate a bit further. The "will"/"be going to" distinction might be attributed to degree of formality. Might it not also relate to a definite/indefinite scale, as in the exercises above? In sentence 13, if "he" does not refer to "No one," there is a hint that the death is anticipated with certainty and only the timing is in doubt. Sentence 11 feels a shade more vague.
I hope the foregoing discussion has satisfied you that time and tense are not the same. If you're left wondering about the tense of "will," it's a present tense verb. You can see the truth of that statement more easily by comparing the present and past tense forms of the following statements:
14. He says that he can sing. / He said that he could sing.
15. He says that he will sing. / He said that he would sing.
I'm sure everyone will agree that "can" is a present tense form and "could" is a past tense form. There is no future tense for "can;" in its present tense, "can" does double duty representing present and future time. What about "will" and "would"? The similarity in form of "could" and "would" is striking, and context confirms that "would" is a past tense form. The only other tense for this verb is "will," which, like "can," is a present tense form and serves for present or future time.